Neurological and mental diseases result, in part, from derangements in regulation of synaptic transmission. In glutamatergic spines, calcium influx through NMDA receptors is a principal regulator of synaptic plasticity. Spines contain many signaling proteins that can be regulated by Ca2+. Different regulatory pathways are activated under different experimental conditions; and, thus, calcium influx can lead to increases or decreases, of varying durations, in synaptic strength. The objectives of the work proposed in this Program Project are to gain a quantitative understanding of Ca2+-regulated signal transduction triggered by Ca2+ in spines, and to apply computational methods to stimulate the dynamics of initial events during Ca2+ signaling in spines. The program includes four projects and a core that will provide new computer software. Project 1 will make use of the computer program Mcell to develop and test models of calcium dynamics in spines based on realistic synaptic geometries and measured spatial distributions and kinetic properties of relevant signaling molecules. The models will be constructed with the use of a streamlined program interface to be developed in the core, and will incorporate data generated in Projects 2 and 4. Project 2 will use quantitative immunocytochemistry at the light and electron microscope levels to study the organization of calcium sources and sinks in spines, as well as the distribution of the Ca2+ target, CaM kinase II. The data will be compared with measurements made in Project 4, and used to constrain simulations arising from Projects 1 and 3. Project 3 will develop and test accurate kinetic models of activation of CaMKII that will be incorporated into the models of Ca2+ dynamics in spines constructed in Project 1. Predictions of simulations of activation of CaMKII will be tested experimentally in conjunction with project 4. Project 4 will use 2-photon fluorescence microscopy to measure [Ca2+] signals and their regulation in individual spines. The data will be integrated with that from project 2, and used to construct and test models made in projects 1 and 3. The program addresses two goals of the Channels, Synapses, and Circuits program of NINDS: 1. To facilitate collaborations among researchers working at molecular and cellular levels to develop multidisciplinary approaches for analysis of channels and synapses and 2. To facilitate collaborations among neuroscientists, computer scientists, and physicists to develop computational tools for data analysis and modeling. The purpose of the models and simulations will be to quantify hypotheses about Ca+ function in spines in order to test them rigorously with experiments. We will attempt to predict the relative importance of measured variations in the structure and molecular composition of synapses for their signaling capabilities. The predictions will be tested by comparison to experiments. Thus, we view the models and the simulations we propose to generate as powerful quantitative tools with which to study the dynamics of synaptic signaling, and not as an end in themselves.